Undifferentiated embryonal sarcoma with unusual features arising within mesenchymal hamartoma of the liver: Report of a case and review of the literature

Undifferentiated embryonal sarcoma (UES) is a rare and highly malignant hep atic neoplasm, affecting almost exclusively the pediatric population. It ha s replaced malignant mesenchymoma, under which diagnostic term the first th ree cases were described. A link between embryonal sarcoma and mesenchymal hamartoma of the liver (MHL) has long been proposed, because of clinicopath ologic overlaps of these entities; however, until recently, this associatio n remained tenuous. Cases of UES arising in a background of mesenchymal ham artoma of the liver have previously been reported in two teenage girls. Dis covery of a similar genetic abnormality in MHL and UES has clinched the sup posed link between them. There have also been two reports of UES with promi nent cystification, one associated with peripheral eosinophilia, and thereb y masquerading as hydatid cyst of the liver. We report a case of UES arisin g in a young boy with MHL, with unusual histologic features, including larg e mesothelial-lined cysts and ectopic adrenal cortical tissue under Glisson 's capsule.